Polymers that contain terminal functional groups are industrially important. One technique to prepare these terminally functionalized polymers is by reaction of a suitable electrophile with a living polymer anion. For numerous examples of end group functionalization chemistry, see Hsieh, H. L.; Quirk, R. P. Anionic Polymerization: Principles and Practical Applications; Marcel Dekker: New York, N.Y., 1996, pages 261-306.
Some of these functionalization reactions are not very efficient, particularly for the preparation of telechelic polymers, due to the formation of a thick gel during the functionalization. This leads to lower capping efficiency. See, for example, U.S. Pat. No. 5,393,843, Example 1, wherein the capping efficiency was only 82%.
A recently reported terminal functionalization technique uses a protected functionalized electrophile. For instance, Nakahama and co-workers have described the reaction of polystyryllithium with the electrophile Br—(CH2)3C(OCH3)3, a protected carboxyl group. See Hirao, A.; Nagahama, H. Ishizone, T.; Nakahama, S. Macromolecules, 1993, 26, 2145. Excellent terminal functionalization of the living anion was achieved (>95%). Other examples of efficient functionalization with protected functionalized electrophiles are reported in Ueda, K.; Hirao, A.; S. Nakahama, S. Macromolecules, 1990, 23, 939; Tohyama, M.; Hirao, A.; Nakahama, S. Macromol. Chem. Phys. 1996, 197, 3135, and Labeau, M. P.; Cramail, H.; Deffieux, A. Polymer International, 1996, 41, 453.
To obtain efficient functionalization, these functionalization reactions are conducted in tetrahydrofuran (THF) at −80° C. THF, however, is an expensive solvent, and these low-temperature conditions are not practical on an industrial scale. In addition, efficient functionalization of polymer anions was only observed with expensive alkyl bromides.